Horizontal conveyor line with workstations

Abstract

The utility model discloses a horizontal conveying line with workstation can be used in shoemaking technical field. The problem that the speed is relatively slow when the carrier changes track in the existing conveying line, and the stability of the movement cannot be guaranteed is solved. The pushing block on the driving line is divided into high pushing block and short pushing block according to the height, a plurality of short pushing blocks are arranged between the two high pushing blocks, the protruding height of the high pushing block on the driving line is greater than the protruding height of the short pushing block on the driving line, the high pushing block is used for applying force to the front force rod, and the short pushing block is used for applying force to the force end of the rear force rod after descending. Thus, when the carrier changes track, the force rod on the carrier can receive the thrust of the short pushing block, the carrier changes track with power, the carrier changes track at high speed, and the stability of the carrier during track changing is good.

Description

Technical Field

[0001] This utility model relates to a horizontally arranged conveyor line for conveying vehicles, and more particularly to a horizontal conveyor line with a workstation. Background Technology

[0002] Conveyor lines are used for long-distance transport of workpieces. Some conveyor lines have several workstations to facilitate workpiece processing, each with one or more processing positions to complete the workpiece handling steps. In some conveyor lines, where large-sized workpieces need to be transported via these workpieces, the spacing between the pushers on the main power line must be adapted to the size of the workpiece, with the distance between the pushers slightly greater than the distance in the direction of travel. In horizontally configured conveyor lines, the workpiece cannot change track using its own power; external power is required for smooth track changes. Such large workpieces require force-bearing rods at both ends. The front force-bearing rod receives the thrust from the pushers, allowing the workpiece to travel on the main rail. During track changes, the front end of the workpiece deviates towards the support rail, while the rear end remains on the main rail. The pushers disengage from the front force-bearing rod, and the rear force-bearing rod at the rear end receives the thrust from the downstream pushers to achieve a smooth track change. If the spacing between the pushers on the main propulsion line is too large, requiring the vehicle to pause and wait at the track change position, the downstream pusher will exert force on the rear force bar of the vehicle again, resulting in a large impact force on the vehicle and affecting its stability. On the other hand, the slow track change speed of the vehicle can also easily obstruct following vehicles, thus increasing the likelihood of rear vehicles colliding with front vehicles, which can easily cause damage and instability to the vehicle.

[0003] Chinese patent document (publication number: CN219468781U) discloses a conveying device for an assembly line, including a driven component, a frame disposed above the driven component, and a loading device disposed on the frame. The driven component comprises a pulley assembly connected below the frame, a connecting block connected below the pulley assembly, and a drive block rotatably connected to the connecting block. A drive rail is provided below the drive block, and the drive rail has protrusions. When the drive block abuts against the protrusions, the drive rail drives the driven component forward. This invention allows for smooth material flow, improves material conveying and storage efficiency, and maximizes the storage of materials in limited space.

[0004] The aforementioned problems are also likely to occur in such conveying devices, which can affect the operational stability of the conveyor line and the safety of the vehicle. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a horizontal conveyor line with a workstation, which has a fast operating speed and can effectively ensure the stability of the vehicle during the track changing process.

[0006] To solve the aforementioned technical problem, the present invention provides the following technical solution: a horizontal conveyor line with a workstation for conveying a vehicle, comprising a horizontally arranged main rail and several branch rails, the branch rails being arranged in a curved shape to form the workstation; the front and rear ends of the vehicle are respectively provided with a front force-bearing rod and a rear force-bearing rod; and further comprising:

[0007] The flexible main power line is set at the position of the main rail to adapt to the direction of the main rail, and several push blocks for propelling the vehicle are set at intervals on the main power line.

[0008] The flexible support line is set at the support rail position to adapt to the direction of the support rail, and several push blocks are set at intervals on the support line to push the vehicle to move on the support rail.

[0009] The station entry device is installed between the inlet end of the branch rail and the main rail to enable the vehicle to autonomously change rails from the branch rail.

[0010] The exit device is installed between the exit end of the branch rail and the main rail to enable the vehicle to change from the branch rail to the main rail;

[0011] The pressure block is set at the track-changing position of the vehicle and is used to apply pressure to the rear force rod so that the force-bearing end of the rear force rod is lowered, so that the force-bearing end of the rear force rod receives the power of the corresponding power line.

[0012] Its features are,

[0013] The push blocks on the main force line include high push blocks and low push blocks. Multiple low push blocks are provided between two adjacent high push blocks. The protrusion height of the high push block on the main force line is greater than that of the low push block on the main force line. The high push block is used to apply force to the front force rod, and the low push block is used to apply force to the force end of the rear force rod after it has descended.

[0014] The main power line and auxiliary power lines are generally structured as link-type drive chains. The main power line propels the vehicle along the main rail, while the auxiliary power line propels it along the auxiliary rails. The main and auxiliary power lines are physically independent, each powered by its own power source. If the vehicle does not need to enter a workstation on the main rail, the entry device does not need to be activated. The vehicle, propelled by the high push block, directly passes the workstation. Although the rear load-bearing rod on the vehicle will lower due to the presence of the pressure block, since the relative position between the vehicle and the main power line generally does not change, the load-bearing end of the rear load-bearing rod will not be subjected to the thrust of the low push block. Alternatively, the pressure block can be positioned so that only the rear load-bearing rod on vehicles requiring track changes can be pressed by the pressure block, lowering its load-bearing end to receive the thrust of the rear low push block.

[0015] Furthermore, along the direction of the vehicle's movement, an entry area, a processing area, and an exit area are sequentially formed on the support rail, with blocking and release mechanisms installed at the downstream ends of each of the three areas; a first sensor for detecting the presence of the vehicle is installed at the entry area; a second sensor for detecting the presence of the vehicle is installed at the processing area; and a third sensor for detecting the presence of the vehicle is installed at the exit area; the first, second, and third sensors are connected to the main controller to enable the vehicle to move in empty space.

[0016] The area is formed on the support rail, i.e. at the work station location, and the blocking and release mechanism and corresponding sensors are set up to facilitate the control of the vehicle's movement at the work station, so that the vehicle's movement at the work station location is orderly and the impact between vehicles is small.

[0017] Furthermore, a front waiting area and a rear waiting area are sequentially formed along the vehicle's direction of travel in the entry area, with two first sensors positioned corresponding to the positions of the front and rear waiting areas, respectively. The establishment of these two waiting areas allows for more refined control of the vehicle, effectively meeting actual operational needs.

[0018] Furthermore, a card reader is installed in the processing area to interpret vehicle information; buttons in the processing area, based on information from a third sensor, control the blocking and release mechanism in the processing area via the main controller, allowing vehicles in the processing area to enter the exit area. The card reader allows for the interpretation of information on the vehicles, enabling operators to verify information before operation and preventing erroneous work.

[0019] Furthermore, a fourth sensor and a pusher sensor are installed on the main rail downstream of the entry device. The pusher sensor detects the high pusher block, and the fourth sensor detects whether there is a vehicle in front of the high pusher block. The blocking and releasing mechanism at the exit area determines whether to allow a vehicle in the exit area to pass through the exit device and enter the main rail based on the information from the fourth sensor and the pusher sensor. By setting up the fourth sensor and the pusher sensor, the vehicle can directly receive the thrust provided by the high pusher block after entering the main rail, preventing collisions on the main rail. This conveyor line has a high degree of automation.

[0020] Furthermore, a magnetic block is installed on the high-push block on the main power line, and the push block sensor is a magnetic sensor. By setting up the magnetic block and magnetic sensor, the position of the high-push block can be sensed, and the structure and control mode are simple.

[0021] Furthermore, an information binding device is installed at the exit area. This device communicates with the main controller and is used to bind the target high-push block to the vehicle to be exited. By setting up the information binding device, the target high-push block and the vehicle are bound together. When controlling the flow of the vehicle subsequently, only the information of the target high-push block needs to be interpreted to determine the vehicle's position. This effectively improves the automation level of the conveyor line and facilitates the correct flow of the vehicle on the conveyor line.

[0022] Furthermore, the first, second, third, and fourth sensors are all photoelectric switches. Photoelectric switches have a simple structure, low manufacturing cost, are easy to install, and are highly sensitive to the position of the vehicle.

[0023] Compared with existing technologies, this utility model has the following advantages: By setting multiple short push blocks between two adjacent high push blocks on the main power line, when the carrier changes track, the downstream short push blocks can quickly abut against the force-bearing end of the rear force-bearing rod on the carrier, thus providing timely track-changing power for the carrier and effectively adapting to the power requirements of track-changing in horizontally set conveyor lines. Because the carrier receives thrust in a timely manner during track-changing, and has a certain initial velocity at the beginning of the track change, the carrier's own potential energy is small. When the corresponding short push blocks apply force to the rear force-bearing rod on the carrier, it does not cause a large impact force on the carrier, thus effectively ensuring the stability of the carrier during track-changing. The presence of multiple short push blocks between two adjacent high push blocks effectively shortens the time for the short push blocks to apply force to the rear force-bearing rod, ensuring the operating efficiency of the conveyor line. When the vehicle is traveling normally on the main rail, the height difference between the high push block and the low push block on the main power line means that the presence of the low push block will not exert force on the forward force rod of the vehicle, and the presence of the low push block will not affect the normal travel of the vehicle on the main rail. Attached Figure Description

[0024] Figure 1 This is a structural diagram of the conveyor line.

[0025] Figure 2 This is an enlarged structural diagram of the workstation.

[0026] Figure 3 This is an enlarged structural diagram of the inbound and outbound devices.

[0027] Figure 4 This is a simplified structural diagram of the workstation.

[0028] Figure 5 It is a structural diagram showing the relative position between the vehicle and the line of force.

[0029] In the diagram: 1. Main rail; 2. Support rail; 21. Outer support rail; 22. Inner support rail; 3. Entering device; 4. Exiting device; 5. Support power line; 6. Swing arm; 7. Mounting base; 8. Front waiting area; 9. Rear waiting area; 10. Blocking and releasing mechanism; 11. First sensor; 12. Second sensor; 13. Third sensor; 14. Card reader; 15. Information binding device; 16. Fourth sensor; 17. Push block sensor; 18. Reader; 19. Carrier; 20. Rear force bar; 201. Upper bar; 202. Lower bar; 21. Front force bar; 22. High push block; 23. Main power line; 24. Low push block. Detailed Implementation

[0030] Referring to the accompanying drawings, the horizontal conveyor of this workstation is horizontally arranged and is used to transport the carrier 19 loaded with workpieces, so that the carrier 19 can enter the workstation to complete the corresponding process at the workstation position.

[0031] The structure of this conveyor line includes a main rail 11 and branch rails 2. The main rail 11 is arranged in a ring shape, and several branch rails 2 are arranged on the outside of the main rail 11. The branch rails 2 are generally U-shaped, and each branch rail 2 forms a workstation. The main rail 11 is horizontally arranged and includes an outer main rail and an inner main rail arranged in parallel. Several breaks are formed on the outer main rail corresponding to the positions of the branch rails 2. Track sections are provided at the break positions. The track sections are adapted to the direction of the outer main rails. Notches are formed between the two ends of the track sections and the two ends of the breaks. The two ends of the track sections are rotatably equipped with swing-arm type entry devices 3 and exit devices 4. The entry devices 3 and exit devices 4 can be bridged within the notches to allow the carrier 19 to pass over the workstation position on the main rail 11. The branch rails 2 are also horizontally arranged, with both ends extending towards the main rail 11. The branch rails 2 include an outer branch rail 21 and an inner branch rail 22 arranged in parallel. At the entry and exit ends of the workstation, the outer support rail 21 and the outer main rail are connected in a curved manner. The entry device 3 bridges with the inner main rail to enable the vehicle 19 to change track from the main rail 11 to the support rail 2; the exit device 4 bridges with the inner main rail to enable the vehicle 19 to change track from the support rail 2 to the main rail 11. The entry device 3 and the exit device 4 have the same structure, except that their orientation differs. Figure 3 The structure is shown in the image. The structure includes a plate-shaped mounting base 7, which is connected to the outer main rail and the outer support rail 21 at a position close to each other. A swing arm 6 is rotatably mounted on the mounting base 7. The swing arm 6 is connected by a motor or cylinder drive to bridge the inner support rail, thereby realizing the track change of the carrier 19.

[0032] This conveyor line is generally used in the shoe manufacturing industry. The front and rear ends of the carrier 19 are respectively equipped with a front force-bearing rod 21 and a rear force-bearing rod 20. A flexible main power line 23 is provided on the lower side of the main rail 11. The main power line 23 is adapted to the direction of the main rail 11. Several push blocks are spaced apart on the main power line 23 to propel the carrier 19 forward. The push blocks apply force to the front force-bearing rod 21 on the carrier 19, thus enabling the carrier 19 to move on the main rail 11. A flexible branch power line 5 is provided on the lower side of the branch rail 2. The branch power line 5 is independent of the main power line 23. The branch power line 5 is adapted to the direction of the branch rail 2. Several push blocks are spaced apart on the branch power line 5. The push blocks act on the front force-bearing rod 21 on the carrier 19, thus propelling the carrier 19 forward on the branch rail 2.

[0033] An interpreter 18 is installed on the main rail 11 upstream of the entry device 3. The interpreter 18 is positioned close to the entry device 3 and is used to interpret the information of the carrier 19, thereby controlling whether the entry device 3 is activated via the main controller. According to the processing path set by the main controller, if the target carrier 19 needs to enter a certain workstation for processing, the entry device 3 in front of that workstation is activated, thus realizing the track change of the carrier 19. After completing a certain process at the workstation, the carrier 19 changes track back to the main rail 11 via the exit device 4, so that the carrier 19 can enter the next workstation according to the predetermined path for the corresponding process. Alternatively, an information binding device 15 can be set on the workstation to indicate that the carrier 19 has completed the corresponding process, so that the main controller can re-set the subsequent path of the carrier 19 until the workpiece on the carrier 19 completes the entire set of processes.

[0034] The force-bearing ends of the front force-bearing rod 21 and the rear force-bearing rod 20 on the carrier 19 are not at the same height. When the carrier 19 passes the track-changing position, the force-bearing end of the front force-bearing rod 21 is lower than the force-bearing end of the rear force-bearing rod 20. When the carrier 19 is traveling normally on the main rail 11, the push block applies force to the front force-bearing rod 21. Due to the position of the force-bearing end, the rear force-bearing rod 20 is not subjected to the pushing force of the push block. Therefore, a pressure block with a certain length is provided on the upstream side of the main rail 11 near the station entry device 3. The pressure block is used to apply pressure to the rear force-bearing rod 20, causing the force-bearing end of the rear force-bearing rod 20 to drop. This allows the rear force-bearing rod 20 to be subjected to the force of the push block when the carrier 19 changes track from the main rail 11 to the branch rail 2. This enables the carrier 19 to change track with power. Correspondingly, a pressure block is also provided on the upstream side of the exit device 4, which is used to apply pressure to the rear force rod 20 when the vehicle 19 changes from the branch rail 2 to the main rail 1, so that the vehicle 19 will receive the thrust of the branch force line 5 when changing rails.

[0035] In the conveyor line, the push blocks on the main power line 23 are divided into high push blocks 22 and low push blocks 24. All the high push blocks 22 on the main power line 23 have the same protrusion height, and all the low push blocks 24 have the same protrusion height. Multiple low push blocks 24 are provided between adjacent high push blocks 22. The protrusion height of the high push blocks 22 on the main power line 23 is greater than that of the low push blocks 24. The high push blocks 22 are used to apply force to the front force-bearing rod 21, and the low push blocks 24 are used to apply force to the force-bearing end of the rear force-bearing rod 20 after it has descended under the action of the pressure block. The rear force-bearing rod 20 is a split structure, including an upper rod 201 movably connected to the carrier 19 and a lower rod 202 hinged at the middle position of the upper rod 201. The lower rod 202 is inclined relative to the upper rod 201, and the lower end of the lower rod 202 is the force-bearing end. A torsion spring is provided at the hinge position of the upper end of the lower rod 202. A protruding part is formed at the lower end of the lower rod 202. The pressure block applies pressure to the protruding part, causing the force-bearing end of the lower rod 202 to descend to the position of the short push block 24 so as to receive the resisting force of the short push block 24.

[0036] See Figure 4The workstation has several functional areas. Along the direction of travel of the carrier 19 on the support rail 2, there are sequentially formed entry area, processing area, and exit area. Each of these three areas has a blocking / releasing mechanism 10 at its downstream end. The blocking / releasing mechanism 10 is generally a blocking component connected to a cylinder. When it is necessary to block the target carrier 19, the blocking component extends to the travel position of the carrier 19 under the action of the cylinder. The blocking component blocks the front force-bearing rod 21 on the carrier 19 by contacting it. The force-bearing end of the front force-bearing rod 21 rises and moves away from the position of the high push block 22, causing the carrier 19 to lose the force applied by the push block on the support power line 5, and the carrier 19 stops in the corresponding area. If the carrier 19 is to move downstream, the blocking component releases its obstruction of the front force-bearing rod 21 under the action of the cylinder. The force-bearing end of the front force-bearing rod 21 descends under gravity, and this force-bearing end receives the force applied by the push block on the support power line 5, thus enabling the carrier 19 to move forward. A first sensor 11 is installed at the entry area to detect the presence of the carrier 19; a second sensor 12 is installed at the processing area to detect the presence of the carrier 19; and a third sensor 13 is installed at the exit area to detect the presence of the carrier 19. The first, second, and third sensors 11, 12, and 13 are connected to the main controller to enable the carrier 19 to move to an empty space. These sensors are generally photoelectric sensors, which can easily detect the presence or absence of the carrier 19 at the corresponding location. The empty space movement refers to the carrier 19 moving to the next location where there is no carrier 19, thus creating an empty space. By dividing these areas, the movement of the carrier 19 on the workstation becomes regular, effectively preventing collisions and damage to the carrier 19 within the workstation. At the entry area, along the direction of the carrier 19's movement, a front waiting area 8 and a rear waiting area 9 are sequentially formed, with the two first sensors 11 positioned corresponding to the positions of the front waiting area 8 and the rear waiting area 9, respectively. Setting up a front waiting area 8 and a rear waiting area 9 allows two vehicles 19 to stop at the entrance area, reducing the pressure on the vehicles 19 on the main rail 11. These two waiting areas can be controlled independently by sensors. When the first sensor 11 in the rear waiting area 9 detects a vehicle 19, the blocking and releasing mechanism 10 in the entrance area can release the vehicle 19 from the front waiting area 8, creating an empty space in the rear waiting area 9. This allows for automatic adjustment of the flow of vehicles 19 on the workstation.

[0037] A card reader 14 is provided in the processing area for interpreting information about the carrier 19. The card reader 14 can be connected to a handheld or fixed display so that the operator can verify the information about the carrier 19 and complete the corresponding process of the workpiece on the carrier 19 according to the instructions on the display. A button is provided in the processing area and is connected to the main controller. When the third sensor 13 does not detect a carrier 19 in the exit area, the operator can press the button, and the main controller will control the blocking and release mechanism 10 in the processing area to allow the carrier 19 in the processing area to enter the exit area. In order to enable the carrier 19 to leave the station with power, a pressure block is also provided at the exit device 4. The pressure block is used to press down the force-bearing end of the lower rod 202 in the rear force rod 20 of the carrier 19 that needs to leave the station, so that the force-bearing end of the lower rod 202 can receive the force of the push block on the support power line 5. The height of the push blocks on the support line 5 can be set at the same height or have different heights.

[0038] A fourth sensor 16 and a push block sensor 17 are installed on the main rail 11 downstream of the entry device 3. The fourth sensor 16 is also a photoelectric switch. The push block sensor 17 is used to sense the high push block 22, and the fourth sensor 16 is used to sense whether there is a carrier 19 in front of the high push block 22. The information from the push block sensor 17 and the fourth sensor 16 are combined. A magnet is provided on the high push block 22, and the push block sensor 17 is a magnetic sensor. Different high push blocks 22 can be distinguished by setting magnets of different sizes on different high push blocks 22. Alternatively, the position of the sensed high push block 22 can be estimated based on the travel speed of the main force line 23, thereby confirming the position reached by the carrier 19, and recording the path traveled by the carrier 19, thus recording which processes the workpiece on the carrier 19 has completed.

[0039] When a vehicle 19 is waiting to exit in the exit area, if the push block sensor 17 detects a high push block 22 passing by, and there is no vehicle 19 in front of the high push block 22, the exit conditions are met. The blocking and releasing mechanism 10 in the exit area will then be activated. The blocking component in the blocking and releasing mechanism 10 will be pushed aside by the cylinder. At the same time, the exit device 4 will be activated and bridged with the inner main rail. The vehicle 19 in the exit area will smoothly change track onto the main rail 11 under the push of the branch power line 5. An information binding device 15 is provided at the exit area. The information binding device 15 is communicatively connected to the main controller and is used to bind the target high push block 22 with the vehicle 19 to be exited. The decoder 18, card reader 14, and information binding device 15 are all based on the identity chip set on the vehicle 19. The identity chip is identified with the identity information of the vehicle 19, such as the number or code of the vehicle 19. The main controller has a preset travel path for the carrier 19, or all the processes that the workpiece on the carrier 19 needs to complete. The station position information is also bound to a certain process. If the carrier 19 passes a certain workstation, the main controller will assume that the workpiece on the corresponding carrier 19 has completed a certain process. There are two modes for the travel path of the carrier 19. One is that the carrier 19 strictly follows the set path. The other is based on logical operations, according to the number of carriers 19 in the conveyor line, selectively sending the carriers 19 to relatively empty workstation positions without process sequence requirements, so as to achieve the balance of carriers 19 in the conveyor line.

Claims

1. A horizontal conveyor line with a workstation for conveying a vehicle, comprising a horizontally arranged main rail and several branch rails, the branch rails being arranged in a curved shape to form the workstation; a front force-bearing rod and a rear force-bearing rod are respectively movably provided at the front and rear ends of the vehicle; further comprising: The flexible main power line is set at the position of the main rail to adapt to the direction of the main rail, and several push blocks for propelling the vehicle are set at intervals on the main power line. The flexible support line is set at the support rail position to adapt to the direction of the support rail, and several push blocks are set at intervals on the support line to push the vehicle to move on the support rail. The station entry device is installed between the inlet end of the branch rail and the main rail to enable the vehicle to autonomously change rails from the branch rail. The exit device is installed between the exit end of the branch rail and the main rail to enable the vehicle to change from the branch rail to the main rail; The pressure block is set at the track-changing position of the vehicle and is used to apply pressure to the rear force rod so that the force-bearing end of the rear force rod is lowered, so that the force-bearing end of the rear force rod receives the power of the corresponding power line. Its features are, The push blocks on the main force line include high push blocks and low push blocks. Multiple low push blocks are provided between two adjacent high push blocks. The protrusion height of the high push block on the main force line is greater than that of the low push block on the main force line. The high push block is used to apply force to the front force rod, and the low push block is used to apply force to the force end of the rear force rod after it has descended.

2. The horizontal conveyor line with a workstation according to claim 1, characterized in that, Along the direction of the vehicle's movement, the support rails form an entry area, a processing area, and an exit area. Each of the three areas has a blocking and release mechanism at its downstream end. A first sensor is installed at the entry area to detect the presence of the vehicle. A second sensor is installed at the processing area to detect the presence of the vehicle. A third sensor is installed at the exit area to detect the presence of the vehicle. The first, second, and third sensors are connected to the main controller to enable the vehicle to move in empty spaces.

3. The horizontal conveyor line with a workstation according to claim 2, characterized in that, Along the vehicle's forward direction, a front waiting area and a rear waiting area are formed sequentially at the entrance area, with two first sensors positioned corresponding to the positions of the front and rear waiting areas, respectively.

4. The horizontal conveyor line with a workstation according to claim 2, characterized in that, A card reader is installed in the processing area to interpret vehicle information; the buttons in the processing area control the blocking and release mechanism in the processing area through the main controller based on the information from the third sensor, so as to allow the vehicle in the processing area to enter the exit area.

5. The horizontal conveyor line with a workstation according to any one of claims 2 to 4, characterized in that, A fourth sensor and a push block sensor are installed on the main rail downstream of the entry device. The push block sensor is used to detect the high push block, and the fourth sensor is used to detect whether there is a vehicle in front of the high push block. The blocking and release mechanism at the exit area determines whether to allow vehicles in the exit area to enter the main rail through the exit device based on the information from the fourth sensor and the push block sensor.

6. The horizontal conveyor line with a workstation according to claim 5, characterized in that, A magnetic block is installed on the high push block on the main power line, and the push block sensor is a magnetic sensor.

7. The horizontal conveyor line with a workstation according to claim 5, characterized in that, An information binding device is installed at the exit area. The information binding device is connected to the main controller and is used to bind the target high-push block with the vehicle to be exited.

8. The horizontal conveyor line with a workstation according to claim 5, characterized in that, The first, second, third, and fourth sensors are all photoelectric switches.

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